The present invention relates to a method for forming a fine-line resist pattern by exposing a resist film to extreme ultraviolet (EUV) radiation through a photomask and also relates to an apparatus for fabricating a semiconductor device by utilizing the pattern forming method.
As semiconductor devices for a semiconductor integrated circuit have been downsized, it has become increasingly necessary to further reduce the feature size of a line-and-space pattern. And to define a fine-line pattern, a lithography technique is indispensable. Particularly when a pattern with a line width of 0.07 μm or less should be defined, a lithography technique using EUV radiation with a wavelength of around 13 nm as an exposing radiation is expected to be very effective.
In a known lithographic process using krypton fluoride (KrF) excimer laser radiation (with a wavelength of around 248 nm) or argon fluoride (ArF) excimer laser radiation (with a wavelength of around 193 nm), an exposure process is carried out in the air or nitrogen ambient. However, if the same exposure process is performed in such an ambient using EUV radiation, then the radiation is absorbed into oxygen or nitrogen molecules contained in the ambient, because the EUV radiation has a much shorter wavelength. This is why the EUV exposure process should be carried-out in a vacuum.
For that reason, a known process of forming a resist pattern out of a chemically amplified resist material, for example, using the EUV radiation is carried out in the following manner.
First, a chemically amplified resist material is applied onto a substrate in the air to deposit a resist film thereon. Next, the resist film is pre-baked to vaporize a solvent contained in the resist film.
Then, the resist film is exposed through a photomask to EUV radiation in a vacuum, thereby transferring the pattern of the photomask onto the resist film.
Subsequently, the resist film is subjected to a post-exposure baking process in the air so that the acid diffuses in the exposed or non-exposed parts of the resist film. Finally, the resist film is developed using a developer, thereby defining a resist pattern.
Where a resist pattern should be formed out of a non-chemically-amplified resist material, the resist film is exposed through a photomask to EUV radiation in a vacuum and then developed immediately in the air without being subjected to the post-exposure baking process.
The present inventor tentatively defined a resist pattern by exposing a resist film to EUV radiation and then patterned a film on a substrate by dry-etching it using the resist pattern obtained. As a result, the present inventor found that the walls of the patterned film showed a non-negligibly high degree of roughness.